This invention relates in general to refrigeration, and in particular relates to refrigeration systems employing liquified carbon dioxide as the coolant.
A number of refrigeration systems have heretofore been developed employing liquified carbon dioxide (LCO.sub.2) to produce refrigeration. The LCO.sub.2 typically is metered through a nozzle or snowhorn into a volume which is to be refrigerated. In another system the LCO.sub.2 is injected through an air amplifier device of the type sold under the name Transvector and which is disclosed in the above-referenced applications Ser. Nos. 818,503 and 838,204.
Among the disadvantages and limitations of previous LCO.sub.2 refrigeration systems is that injection of the coolant through a nozzle or snowhorn causes some of the liquid to flash to solid CO.sub.2, known as dry ice or snow. The resulting plume of gas and snow is at a relatively cold temperature on the order of -110.degree. F. so that it is difficult to control the temperature of the refrigerated volume. Also, deposit of the snow on certain food products can create localized freezing or "freezer-burn", which is highly objectionable from the standpoint of product degradation and spoilage. Certain systems have employed exhaust fans in an attempt to remove the snow and prevent the freezer-burn, but this has not been completely successful and moreover increases equipment and operating cost.
Typically LCO.sub.2 refrigeration systems heretofore have required the use of a gas purge system to ensure that the nozzles or snowhorns do not become blocked by buildup of solid CO.sub.2. The requirement of a gas supply and piping for the purge system increases the equipment and operating costs, and in addition is a source of malfunction and increases maintenance requirements.
Refrigeration systems employing Transvectors also have limitations and shortcomings. While the use of Transvectors for transforming the LCO.sub.2 into a gas reduces the problem of dry ice buildup in certain cases, it is not completely successful with the result that over a period of time there can be an objectionable accumulation of dry ice in the refrigeration zone and on the product. In addition the Transvector devices employed in such systems are relatively complicated, bulky and expensive.